1. Field of the Invention
This invention relates to a wafer probing system, more particularly it relates to a wafer probing system for probing electric characteristics of circuit patterns formed on a semiconductor wafer.
2. Description of the Related Art
As for a semiconductor wafer, a multiplicity of same circuit patterns are formed according to the kind of the wafer. Each circuit pattern is judged whether it is good or bad by the probe card of the wafer probing system for probing the electric characteristics of each circuit pattern before the wafer is separated into individual dies.
In the wafer probing system, when the same kind wafers are probed, an alignment is performed in the first wafer and the electrode pad of the second and after wafer circuits are touched to the probe needle of the probe card certainly based on the result of the alignment.
That is, in the alignment method, as shown in FIG. 2, the first wafer 3 is held by a table 2 which is placed on the main body 1 of a wafer probing system movably and the table 2 is moved to a predetermined position under a CCD camera 4.
Next, a reference pattern among the plural alignment patterns formed on the wafer 3, which becomes a standard, is picked up with the CCD camera 4, and then the reference pattern is memorized as a model data in a RAM 5a of an image processing device 5.
Then, the table 2 is moved in the direction of a probe card 6, probe needles 7 of the probe card 6 are touched to an electrode pads of the circuit patterns on the wafer 3 and a movement value L to the touched (probed) position is memorized in a RAM 8a of a prober control part 8. And, in the first wafer 3, each circuit pattern is probed based on the position in which the electrode pads touch the probe needles 7.
As for the second and after wafers 3, first, the table 2 is moved by using a known correlation method and the like so as to pick up the same circuit pattern as the reference pattern of the model data memorized in the RAM 5a with the CCD camera 4. Next, the table 2 is moved by the movement value L memorized in the RAM 8a- Therefore, the second and after wafers 3 are moved to the position where the electrode pads touch the probe needles 7. With this arrangement, the second and after wafers 3 are aligned based on the model data and the movement value memorized concerning the first wafer 3.
However, in the alignment method in the conventional wafer probing system, for instance, when a wafer of A kind is probed and then a wafer of B kind is probed, the reference pattern and the movement value to the probed position of the A kind are deleted from the RAM 5a and 8a, therefore, when the wafer of A kind is probed again, a new reference pattern and a new movement value to the probed position must be obtained. Thus, there is a disadvantage in that the wafer can not be probed efficiently.